I recall a lengthy discussion about this once on a another forum and it's amazing how many variations from the normal old "Lowepro" people use for camera bags. My two (ten?) bits - I searched high and low (hither and yon) for something that was durable, roomy, discreet and didn't look like a camera bag for which ever kit I was out with at the time. I wanted a Domke, liked the style, but couldn't find just the right one - and didn't want to pay $220 in any case.
I ended up finding two really nice canvas Fossil bags that are ideal and have held the test of time exceedingly well. They were called "Meesenger Bags", but look nothing like those flat, structured bags I think of when I think of messenger bag, plenty of "girth" for Hassy and stuff and even my Field camera and accsys. and protect as well or better as a Domke (I finally got a small one, then sold it).
These really high quality and made of thick, soft canvas with thick, real leather trim and are large enough for all I need. Both have three large soft dividers and many smaller pockets. Straps are comfortable, easy adjust 2" wide canvas webbing and plenty long enough. All trim is triple stitched and slightly distressed real leather - GOOD leather too, no VINYL to be found - and the canvas is heavy enough to repel moderate weather for an hour or two. One of em looks similar to the photo, but in Khaki. Neither looks even remotely like a "Man Purse" in case you were concerned about that...I paid $20 each on clearance for them. They can be got new for about a bill. There is no other camera bag at any price I'd rather have then these for out walking around.
I always feel like I have to evangelize a bit about these bags, as I feel no other photographer has 'discovered' Fossil as camera bag yet. Maybe I'm the only one who likes these?